1. Field of the Invention
This invention relates to a roll-over suppressing control apparatus for a vehicle which causes, when the vehicle is placed into an excessive rolling state upon turning thereof, braking force to be applied to wheels to carry out roll-over suppressing control.
2. Description of the Related Art
As a technique for controlling the posture of a vehicle upon turning, a technique has been developed wherein a rolling state of the vehicle body is detected and, when the rolling of the vehicle body is excessively great, braking force is applied to particular wheels to suppress rolling of the vehicle thereby to suppress roll-over (turning over on its side) of the vehicle (refer to, for example, Japanese Patent Laid-Open No. Hei 11-11272).
According to the technique, when a roll rate (rolling angular velocity of the vehicle body is detected and the detected roll rate is equal to or higher than a predetermined value or when a steering angular velocity is arithmetically operated based on a steering angle detected by a steering angle sensor and the arithmetically operated steering angular velocity is equal to or higher than a predetermined value, the brake system of the vehicle is controlled to suppress rolling of the vehicle body.
In order to suppress rolling of a vehicle, it is effective to lower the speed of the vehicle.
Incidentally, according to the technique wherein braking force is applied to suppress roll-over as described above, since the vehicle speed is lowered against the will of the speed of the driver in order to suppress roll-over, it is not desired to carry out the roll-over suppressing control unnecessarily. Therefore, it is important to set conditions for starting the roll-over suppressing control, and it is desired to carry out such control only when the possibility takes place that roll-over may occur.
While the prior art described above adopts such logic that roll suppressing control is started when the magnitude of the roll rate exceeds a predetermined value (a certain fixed value), it seems that this is based on an idea that the magnitude of the roll rate indicates the possibility of roll over (degree of turning over on its side) of the vehicle.
However, the relationship between the roll rate (or the value of some other parameter representative of a rolling state of the vehicle) and the degree of turning over on its side of the vehicle is not always fixed, but actually differs depending upon the turning situation. Therefore, where the roll suppressing control is started when the magnitude of the roll rate exceeds a fixed value as in the prior art, the roll suppressing control may sometimes be carried out unnecessarily depending upon the turning situation or, although it is necessary to start the roll suppressing control, the roll suppressing control may not sometimes be started.